The present invention relates to a process for defining and modifying a partition on a storage space of a non-erasable carriers or media. The latter are in particular used for the archival storage of voluminous information, because they are not very expensive. They are increasingly used in the archival storage of digitized documents and files.
The digital optical disk is an example of a non-erasable carrier. On such a carrier it is possible to write an information at any time, but it is not possible to modify a written information. Such a carrier is said to be of the "WORM" type.
The digital optical disk is a large capacity non-erasable carrier. For an effective management or control of said large storage space, it is standard practice to subdivide it into segments of different sizes. This offers greater security and greater flexibility of use of the digital optical disk. Moreover, the digital optical disk is a detachable support which can be transported between a storage area and a reader. It must therefore be provided with reliable and transportable identification mechanisms.
Various methods are known for identifying a non-erasable carrier and for segmenting the storage space thereof.
With regards to the identification, the currently used method consists of writing a header or heading information at a precise location of the storage space, generally the first sector in the case of a non-erasable carrier organized into sectors. This header information is unique and is read back during the fitting operation of the non-erasable carrier, i.e. when the disk is loaded into a reader.
The fact of having a unique header is a disadvantage because if it is not possible to read back the location containing the header as a result of a fault on the non-erasable carrier, the header information cannot be used and cannot be regenerated. Another disadvantage is that as the header is only written once, it cannot store informations which evolve, such as the filling level of the storage space of the non-erasable carrier.
On the non-erasable carrier, the stored information is e.g. organized into files. With each file is associated two information types which are, on the one hand, the file description informations and, on the other, information representing the actual content of the file. The description information is much less voluminous than the content information.
Various methods are known for recording files on a non-erasable carrier. For each segment, said methods are based on a sequential allocation of the memory in this segment, e.g. by a sequential allocation of the sectors in the case of a digital optical disk.
According to a first known method, all the storage space of the non-erasable carrier is looked upon as a single segment. The description information and the content information are then sequentially written and are consequently interleaved in the same segment, as shown in FIG. 1.
This method suffers from at least two disadvantages. Firstly the access time to a description information is greatly increased by the passage time of the content information, which is generally voluminous. Secondly the complete sequential passage of the description information makes it necessary to pass through all the information. This passage, which can e.g. be required during the fitting of a non-erasable carrier to a reader, then requires a very considerable amount of time.
A second method is known, in which the description information and content information are stored in different segments. More precisely, the storage space of the non-erasable carrier is subdivided into two segments, as shown in FIG. 2.
The first segment starts at one of the ends of the storage space of the non-erasable carrier and the allocation of said segment takes place sequentially on the basis of this starting point. The second segment starts at the other end of the storage space of the non-erasable carrier and its allocation starts sequentially from said point.
This second method permits a more effective management of the non-erasable carrier than the first method. However, all the description information is stored in the same segment. This is not satisfactory because the description information can be of different types and volumes.
A third method is also known, in which the storage space of the non-erasable carrier is broken down into N segments, as shown in FIG. 3. This takes place during the formatting of the non-erasable carrier and cannot subsequently be further modified. This third method is of interest when it is possible to forecast from the outset the number and size of segments which will be useful. In the opposite case, this method leads to a loss of storage spaces for the carrier.